Pride, a lack of humility.
Ulysses shows that he is prideful when he boasts to Polyphemus that he has defeated him. Instead of keeping his name a secret, he tells the cyclops his real name and asks that he tell everyone that he, Ulysses, was the one who blinded and shamed him. This doesn't go well for Ulysses as the cyclops then asks his father, Poseidon, to prevent Ulysses from returning home. Thus begins Ulysses very long journey to Ithaca.
